(1) Field of the Invention
This invention relates to a method for producing p-isobutylstyrene. More particularly, the invention relates to a novel method via a new compound for economically producing the above compound in a pure form. From the above p-isobutylstyrene (hereinafter referred to as "PBS"), .alpha.-(p-isobutylphenyl)propionic acid is derived, which is known as a useful medicine (Ibuprofen, trade name) for the relief of pain, fever and inflammation.
(2) Description of the Prior Art
In order to prepare PBS in a pure form at low cost, the following conditions are required:
(a) To use simple compounds as starting materials;
(b) To employ fewer steps of reactions in which intermediate compounds are also simple and stable;
(c) To employ reactions that do not cause isomerization because the isobutyl group is liable to be isomerized; and
(d) To use inexpensive reagents and catalysts.
There are disclosed several methods for producing p-isobutylstyrene (PBS) in U.S. Pat. No. 4,329,507.
For example, .alpha.- or .beta.-(p-isobutylphenyl)ethyl alcohol is dehydrated and .alpha.- or .beta.-(p-isobutylphenyl)ethyl chloride or .alpha.- or .beta.-(p-isobutylphenyl)ethyl bromide is dehydrohalogenated to obtain PBS. In these methods, however, intricate and expensive substances are used as starting materials or unstable and intractable reagents such as Grignard reagents are used so that these methods cannot be regarded as inexpensive and economical.
For example, PBS is prepared by dehydration of .alpha.-(p-isobutylphenyl)ethyl alcohol which is obtained by the reduction of p-isobutylacetophenone, which process is one of most preferable ones. Namely, in this process, p-isobutylacetophenone is used as a starting material.
The p-isobutylacetophenone, however, is not an inexpensive compound as described below. It is most economical to synthesize the p-isobutylacetophenone from isobutylbenzene but the conversion itself of isobutylbenzene into p-isobutylacetophenone is not desirable in an economical view point. That is, an expensive and unstable material of acetyl chloride must be used in the conversion into p-isobutylacetophenone. In addition, a large quantity of, i.e. at least equimolecular amount (to acetyl chloride) of anhydrous aluminum chloride that is quite susceptible to moisture, must be used. For example, assuming that the conversion rate is stoichiometrically 100%, anhydrous aluminum chloride as much as 700 kg is to be used for producing 1,000 kg of p-isobutylacetophenone. In addition, waste materials of 410 kg of aluminum hydroxide and 750 kg of chlorine ions are produced as a result of the deactivation of anhydrous aluminum chloride and the waste materials that exceed the quantity of aimed p-isobutylacetophenone must be treated into innoxious substances. Accordingly, it goes without saying that p-isobutylacetophenone is quite expensive as a starting material.